Closed-loop upcycling strategy for regenerating high-performance NCM523 cathodes via tannic acid-assisted low-temperature hydrothermal method with in-situ aluminum doping

The growing wave of retired lithium-ion batteries presents severe resource and environmental challenges, making direct recycling an increasingly prominent solution. However, the inherent contradiction between the limited cycle life of batteries and the rapidly evolving technological demands is driving a paradigm shift in the field—from traditional “direct recycling” toward more value-added “direct upcycling.” In this study, we developed a closed-loop upcycling strategy based on tannic acid-assisted low-temperature hydrothermal relithiation combined with Al doping-coating derived from current collector fragments. This approach innovatively employs tannic acid as a low-cost, low-concentration redox mediator, significantly enhancing the relithiation kinetics of spent NCM materials and reducing the complete relithiation temperature from 220 °C to 140 °C, thereby efficiently restoring the structural integrity of the cathode. Furthermore, aluminum impurities were converted into functional components, and by precisely controlling the Al content, simultaneous lattice doping and surface coating were achieved in the spent NCM523 cathode, establishing a dual bulk-interface enhancement mechanism. Benefiting from this synergistic modification, the regenerated material exhibits outstanding electrochemical performance: a specific discharge capacity of 169.61 mAh g−1 at 0.1C, and remarkable cycling stability even at a high cut-off voltage of 4.5 V.